The present invention relates to a method for preparing an oxazole. More particularly, the invention is concerned with a novel method for preparing 5-cyano-4-methyl-oxazole which is an important intermediate in the manufacture of Vitamin B.sub.6.
Heretofore, 5-cyano-4-methyl-oxazole has been obtained by reacting 5-carbamoyl-4-methyl-oxazole with phosphorus pentoxide heated to fusion temperature. However, various disadvantages are associated with this process. In particular, the yield is relatively low. An improvement in this process consists in carrying out the reaction of phosphorus pentoxide with 5-carbamoyl-4-methyl-oxazole in the presence of a solvent, namely quinoline. This improved process, has, however, the disadvantage that quinoline is insufficiently stable under the reaction conditions, has a disagreeable odour and is noxious. Further, the procedure for regenerating the quinoline and for working-up the product resulting from the phosphorus pentoxide to an environmentally acceptable product is expensive and encumbered with a series of technological problems. Moreover, not only quinoline but also phosphorus pentoxide is expensive and commercially scarce.
Another improvement in the manufacture of 5-cyano-4-methyl-oxazole consists in reacting 5carbamoyl-4-methyl-oxazole with a lower alkanecarboxylic acid anhydride and subjecting the reaction mixture or the 5-[N-(lower alkanoyl)-carbamoyl]-4-methyl-oxazole isolated from the latter to a pyrolysis. This pyrolytic process has certain disadvantages such as, in particular, high working temperatures, great problems with the materials from which the reactor may be constructed and formation of byproducts which are difficult to recycle.